Field of the Invention
The present invention relates to light source optimizing methods, exposure methods, device manufacturing methods, programs, exposure apparatuses, lithography systems, light source evaluation methods, and light source modulation methods, and more particularly to a light source optimizing method to optimize a shape of an illumination light source which is used to form a pattern on an object, an exposure method using the light source optimizing method, a device manufacturing method using the exposure method, a program which makes a computer used for control of an exposure apparatus execute a processing to optimize a shape of an illumination light source, an exposure apparatus which irradiates an illumination light to form a pattern on an object, a lithography system which includes the exposure apparatus, a light source evaluation method suitable to optimize a shape of an illumination light source, and a light source modulation method to modulate a luminance distribution of an illumination light source.
Description of the Background Art
With finer device patterns, projection exposure apparatuses used to manufacture semiconductor devices and the like, as in a so-called stepper or a so-called scanning stepper (also called a scanner), have come to require high resolution. Resolution R is expressed in the Rayleigh equation, that is, R=k1 (λ/NA). Here, λ is the wavelength of a light source (illumination light), NA is the numerical aperture of a projection optical system, and k1 is the process factor determined by resolvability and/or process controllability of a resist. Because of this, conventionally, attempts have been made to improve resolution by making wavelength λ of the illumination light shorter and making the numerical aperture of the projection optical system larger (higher NA). However, because pursuing shorter exposure wavelengths present difficulties when developing light sources and glass material, and higher NA reduces the depth of focus (DOF) of the projection optical system which degrades the image-forming performance (image-forming characteristics), higher NA cannot be pursued more than is necessary.
Due to such reasons described above, only shortening the wavelength of wavelength λ of the illumination light and increasing the numerical aperture (higher NA) of the projection optical system were not enough to keep up with finer circuit patterns and sizes. Therefore, efforts were put into improving the lithography performance (lower k1) by using modified illumination technology such as annular illumination in an exposure apparatus, introducing technology such as phase-shift mask for extending the limits of optical lithography, and in resist technology, by developing raw materials and using process development technologies such as thinner film formation and multiple layer formation.
In recent years, as a means of further realizing higher NA, an exposure apparatus is put to practice which employs a local liquid immersion exposure technology, however, also in the liquid immersion exposure apparatus, because there are limitations not only to a shorter wavelength of wavelength λ of the illumination light but also to a higher NA, a lower k1 has become absolutely essential. With lower k1 in recent years, not only are super-resolution technologies such as modified illumination and phase-shift technology used, but also optical proximity effect correction (OPC: Optical Proximity Correction) requires consideration, where degradation in a pattern fidelity which occurs due to an optical system error such as aberration or when a reticle pattern is transferred onto a wafer is corrected, using a reticle pattern. However, because lower k1 reduces the contrast of the pattern image, this point also needs attention.
Under such background, to provide an optical imaging solution which allows mass-production at a low k1 value, SMO (Source and Mask Optimization) in which a pattern of a mask (reticle) and an illumination light source are simultaneously optimized by an optical model is recently gathering attention. SMO is disclosed, for example, in U.S. Pat. No. 6,563,566 and the like. Light source intensity distribution output from SMO is realized, for example, by a spatial light modulator (SLM: Spatial Light Modulator) disclosed in U.S. Patent Application Publication No. 2009/0097094 and the like.
However, between a target light source intensity distribution and the actual light source intensity distribution, a deviation occurs due to various kinds of errors. By this deviation, image-forming performance, especially optical proximity effect (OPE: Optical Proximity Effect) results differently from the target value (OPE error occurs). In the conventional image-forming optical system, parameters to correct the OPE errors were relatively simple as in the NA of a projection optical system, illumination σ, and annular ratio and the like. Therefore, it was relatively easy to perform the OPE matching.
However, the actual case is that it is difficult to perform an effective the OPE matching of a complicated illumination intensity distribution like an SMO solution with highly flexible parameters such as SML.